### Home Classes Methods

### In Files

- lib/packetfu/capture.rb

### Parent

Object

### Methods

- ::new
- #bpf
- #capture
- #clear
- #next
- #save
- #setup_params
- #show_live
- #start
- #w2a
- #wire_to_array

### Files

- .document
- README.rdoc

### Class/Module Index

Quicksearch

- PacketFu
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# PacketFu::Capture

The Capture class is used to construct PcapRub objects in order to collect packets from an interface.

This class requires PcapRub. In addition, you will need root (or root-like) privileges in order to capture from the interface.

Note, on some wireless cards, setting :promisc => true will disable capturing.

## Example

    # Typical use
    cap = PacketFu::Capture.new(:iface => 'eth0', :promisc => true)
    cap.start
    sleep 10
    cap.save
    first_packet = cap.array[0]

    # Tcpdump-like use
    cap = PacketFu::Capture.new(:start => true)
    cap.show_live(:save => true, :filter => 'tcp and not port 22')

## See Also

Read, Write

### Attributes

array[RW]
filter[R]
iface[R]
promisc[R]
snaplen[R]
stream[RW]
timeout[R]

### Public Class Methods

new(args={}) click to toggle source

    # File lib/packetfu/capture.rb, line 31
    def initialize(args={})
            @array = [] # Where the packet array goes.
            @stream = [] # Where the stream goes.
            @iface = (args[:iface] || ENV['IFACE'] || Pcap.lookupdev || "lo").to_s
            @snaplen = args[:snaplen] || 0xffff
            @promisc = args[:promisc] || false # Sensible for some Intel wifi cards
            @timeout = args[:timeout] || 1
            @filter  = args[:filter] || args[:bpf]
            setup_params(args)
    end

### Public Instance Methods

bpf(args={}) click to toggle source

bpf() sets a bpf filter on a capture session. Valid arugments are:

    :filter
      Provide a bpf filter to enable for the capture. For example, 'ip and not tcp'

    # File lib/packetfu/capture.rb, line 100
    def bpf(args={})
            filter = args[:filter] || args[:bpf] || @filter
            capture if @stream.class == Array
            @stream.setfilter(filter) if filter
            @filter = filter
    end

Also aliased as: filter
capture(args={}) click to toggle source

capture() initializes the @stream varaible. Valid arguments are:

    :filter
      Provide a bpf filter to enable for the capture. For example, 'ip and not tcp'
    :start
      When true, start capturing packets to the @stream variable. Defaults to true

    # File lib/packetfu/capture.rb, line 56
    def capture(args={})
            if Process.euid.zero?
                    filter = args[:filter] || args[:bpf] || @filter
                    start = args[:start] || true
                    if start
                            begin
                                    @stream = Pcap.open_live(@iface,@snaplen,@promisc,@timeout)
                            rescue RuntimeError
                                    $stderr.print "Are you sure you're root? Error: "
                                    raise
                            end
                            bpf(:filter=>filter) if filter
                    else
                            @stream = []
                    end
                    @stream
            else
                    raise RuntimeError,"Not root, so can't capture packets. Error: "
            end
    end

clear(args={}) click to toggle source

clear() clears the @stream and @array variables, essentially starting the capture session over. Valid arguments are:

    :array
      If true, the @array is cleared.
    :stream
      If true, the @stream is cleared.

    # File lib/packetfu/capture.rb, line 89
    def clear(args={})
            array = args[:array] || true
            stream = args[:stream] || true
            @array = [] if array
            @stream = [] if stream
    end

next() click to toggle source

next() exposes the Stream object's next method to the outside world.

    # File lib/packetfu/capture.rb, line 127
    def next
            return @stream.next
    end

save(args={}) click to toggle source

save() is a equivalent to wire_to_array()

    # File lib/packetfu/capture.rb, line 137
    def save(args={})
            wire_to_array(args)
    end

setup_params(args={}) click to toggle source

Used by new().

    # File lib/packetfu/capture.rb, line 43
    def setup_params(args={})
            filter = args[:filter] || args[:bpf] || @filter
            start = args[:start] || false
            capture if start
            bpf(:filter=>filter) if filter
    end

show_live(args={}) click to toggle source

show_live() is a method to capture packets and display peek() data to stdout. Valid arguments are:

    :filter
      Provide a bpf filter to captured packets.
    :save
      Save the capture in @array
    :verbose
      TODO: Not implemented yet; do more than just peek() at the packets.
    :quiet
      TODO: Not implemented yet; do less than peek() at the packets.

    # File lib/packetfu/capture.rb, line 151
    def show_live(args={})
            filter = args[:filter] || args[:bpf] || @filter
            save = args[:save]
            verbose = args[:verbose] || args[:v] || false
            quiet = args[:quiet] || args[:q] || false # Setting q and v doesn't make a lot of sense but hey.

            # Ensure the capture's started.
            if @stream.class == Array
                    capture
            end

            @stream.setfilter(filter) if filter
            while true
                    @stream.each do |pkt|
                            puts Packet.parse(pkt).peek
                            @array << pkt if args[:save]
                    end
            end
    end

start(args={}) click to toggle source

start() is equivalent to capture().

    # File lib/packetfu/capture.rb, line 78
    def start(args={})
            capture(args)
    end

w2a(args={}) click to toggle source

w2a() is a equivalent to wire_to_array()

    # File lib/packetfu/capture.rb, line 132
    def w2a(args={})
            wire_to_array(args)
    end

wire_to_array(args={}) click to toggle source

wire_to_array() saves a packet stream as an array of binary strings. From here, packets may accessed by other functions. Note that the wire_to_array empties the stream, so multiple calls will append new packets to @array. Valid arguments are:

    :filter
      Provide a bpf filter to apply to packets moving from @stream to @array.

    # File lib/packetfu/capture.rb, line 116
    def wire_to_array(args={})
            filter = args[:filter] || args[:bpf] || @filter
            bpf(:filter=>filter) if filter

            while this_pkt = @stream.next
                    @array << this_pkt
            end
            @array.size
    end

[Validate]

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